The present invention relates to power steering devices for use in motor vehicles, etc.
In order to lighten the steering operation, the motor vehicles use a power steering device for producing a steering assisting force by supplying/discharging working fluid to/from an actuator of a steering unit.
Various improvements have been proposed in the power steering devices. By way of example, JP-U 56-59474 discloses a power steering device comprising a pressure switch arranged in a hydraulic circuit between an actuator including a control valve and a power cylinder and a hydraulic pump driven by a drive source so as to detect the pressure within the hydraulic circuit and an accumulator. When the pressure within the hydraulic circuit is less than a predetermined value, the hydraulic pump is driven by the drive source, and when it is more than the predetermined value, the operation of the hydraulic pump by the drive source is stopped.
This improved power steering device can avoid an inconvenience due to insufficient discharge of working fluid produced upon quick steering, etc. by a rise characteristic of the hydraulic pump by previously accumulating working fluid in the accumulator. This device can also achieve energy saving by driving the hydraulic pump discontinuously, i.e. only when the pressure switch detects a pressure drop within the hydraulic circuit.
With the known power steering device, however, the hydraulic pump is driven when the pressure within the hydraulic circuit is less than the predetermined value, so that when a hydraulic system produces an inconvenience such as leakage of working fluid from a hydraulic pipe, the hydraulic pump can be driven continuously to consume power uselessly. The same problem can arise when the pressure switch for detecting the pressure within the hydraulic circuit produces an inconvenience.
Regarding the problem that the hydraulic pump is driven continuously to consume power uselessly, it is noted that an anomaly of the hydraulic system can be determined by monitoring the pressure within the hydraulic circuit, and an anomaly of an electric system can be determined in accordance with a signal of the pressure switch itself for monitoring the pressure within the hydraulic circuit. This means that both anomalies can be determined in accordance with a signal of the pressure switch.
It is, therefore, an object of the present invention to provide power steering devices which can minimize useless power consumption by early detection of an anomaly of the hydraulic or electric system thereof.